The invention relates to a distance measuring instrument with a sighting device. The invention also relates to a method for detecting a spot on an object being measured whose distance is to be determined.
Distance measuring instruments of this generic type are well known in the prior art. They have a distance measuring range of several tens of meters and are often embodied as handheld instruments. They are used primarily in construction surveying or in interior renovation, for instance for measuring rooms in three dimensions. Other areas of application for distance measuring instruments are geodetic and industrial surveying. The fundamental principle of distance measurement with the known instruments is based on evaluating a change over time in a characteristic variable of the electromagnetic radiation emitted by the instrument and remitted by an object sighted. To that end, the distance measuring instrument is equipped with a transmitter for emitting an intensity-modulated radiation. In handheld instruments, this is primarily an optical radiation in the visible wavelength spectrum, to make it easier to aim at the measurement spots. The optical radiation is remitted or scattered by the object being measured aimed at and is recorded by a receiver built into the instrument. From the time lag of the modulated radiation received compared to the radiation emitted by the transmitter, the distance from the object being measured is found.
In indoor rooms, the visible radiation used in handheld instruments, generally laser radiation, is readily apparent to the eye on the object being measured. However, if light shines intensively on the object being measured, the eye has difficulty in distinguishing the spot from the background. This is particularly true in outdoor applications, in which the object being measured is often exposed to quite intensive sunshine, and the spot remitted by the object being measured can often be perceived only with difficulty, if at all, by the naked eye. To overcome this problem, users of the distance measuring instrument sometimes put on glasses provided with optical filters, which allow only the measurement radiation reflected by the object being measured to pass through them. The special glasses used for this purpose are at high risk of breaking and are often not directly at hand, and the user often finds them annoying and bothersome. In known distance measuring instruments, telescopic sights that can be mounted on the instrument are also known as an alternative way of solving this problem. These telescopic sights are intended to help the user of the distance measuring instrument recognize the spot on the object being measured to be surveyed or measured. Telescopic sights are also already known that are additionally provided with special filters that are attuned to the light of the spot. Telescopic sights can be complicated and expensive. In particular, telescopic sights or similar optical sighting aids are calibrated with the laser beam. This makes such instruments very vulnerable to shock. To overcome this disadvantage and not unnecessarily increase the weight of the distance measuring instrument, the telescopic sight is often embodied as a separate part, which is to be mounted on the distance measuring instrument only when needed, and which must then be calibrated. The separate distance measuring instrument is vulnerable to damage. Often, the user fails to carry it with him, or it gets lost entirely. After being mounted, it must first be recalibrated with the laser beam.